1. Field of the Invention
The present invention relates to an optical wavelength converter.
2. Description of the Related Art
There is known a channel type optical wavelength converter having a LiNbO.sub.3 layer dispersed with Ti strip layers on a substrate made of yttrium (Uesugi "Optical wavelength converter using a LiNbO.sub.3 waveguide" Japanese Journal of Applied Physics Vol. 49, No. 12, PP. 1234-1238, 1980).
In this type optical wavelength converter, it is necessary to conduct phase matching of the fundamental wave and the second harmonic for improving its conversion efficiency. The phase matching is obtained by a method of changing the refractive index in response to changes of temperature, by a method that both the equivalent refractive indexes to a propagating fundamental wave and the second harmonic are coincident in a single waveguide of the optical wavelength converter, or the like. The optical wavelength converter that uses the former technique, in which the phase matching is controlled by the change of temperature, is necessarily provided with a device for controlling temperature adjacent to the converter to avoid the influence of outside temperature changes. The device for controlling temperature utilizes the Peltier effect and keeps the temperature of the optical wavelength converter constant.
However, this device for controlling temperature has a problem that and its response is slow due to the fact that the time constant of the device is large, since the temperature of the device is subject to the outside changes in temperature. Furthermore, this device for controlling temperature requires a large amount of electric current to be driven sufficiently.